Nikon D700 - Manual (Page 210)

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The Built-in Flash
The built-in flash has a Guide Number (GN) 17/56 (m/ft, ISO 200,
20 °C/68 °F) and can cover the field of view of a 24mm lens, or a
16mm lens in DX format. It supports i-TTL balanced fill-flash for
digital SLR, which uses monitor pre-flashes to adjust flash output
for balanced lighting not only when natural lighting is inadequate
but when filling in shadows and backlit subjects or adding a catch
light to the subject’s eyes. The following types of i-TTL flash
control are supported:
D ISO Sensitivity
i-TTL flash control can be used at ISO sensitivities between 200 and 6400.
At values over 6400 or under 200, the desired results may not be achieved
at some ranges or aperture settings.
i-TTL balanced fill-flash for digital SLR : Speedlight emits series of nearly
invisible preflashes (monitor preflashes) immediately before main flash.
Preflashes reflected from objects in all areas of frame are picked up by
1,005-segment RGB sensor and are analyzed in combination with range
information from matrix metering system to adjust flash output for
natural balance between main subject and ambient background
lighting. If type G or D lens is used, distance information is included
when calculating flash output. Precision of calculation can be increased
for non-CPU lenses by providing lens data (focal length and maximum
aperture; see pg. 210). Not available when spot metering is used.
Standard i-TTL flash for digital SLR : Flash output adjusted to bring lighting in
frame to standard level; brightness of background is not taken into
account. Recommended for shots in which main subject is emphasized
at expense of background details, or when exposure compensation is
used. Standard i-TTL flash for digital SLR is activated automatically when
spot metering is selected.